Temperature Sensing


I want to automate the water motor switching on and switching off, when water comes in morning

Solution I have in mind:

Affix a diode to the water pipe, and affix another to a nearby body, now make a circuit that compares the temperatures and turn a relay on and off accordingly.

Suggestion needed:

Can someone recommend me a good electrical component to sense temperature, I was thinking to use a regular diode (1N4001) that are available at electronics labs, if anyone got a better suggestion please tell, the code of that electronic component (which is common enough to be available at college road).

EDIT: I found out that using LM35 can be more accurate, it gives 10mv difference per Celsius